Cathode assembly



Sept. 12, 1950 L. A. BACKER ETAL CATHODE ASSEMBLY Filed May 21, 1948 W m N MP M55, T KP m T M 1 Am UM Y B Patented Sept. 12, 1950 UNITED STATES PATENT OFFICE assignors to Federal Telephone and Radio Corporation, New York, N. Y.,

J r., Rutherford, N. J

a corporation of Delaware Application May 21, 1948, Seria1 No.

e Clainis- (01. 250-275) Our' invention relates to electron discharge devices and deals particularly with cathode structur'es for electron discharge devices of the. large or power class.

The cathode electrode of a power tube is often fabricated from a number of parallel straight filamentary cathodes disposed cylindrically and coaxially with a cylindrical grid and anode. vIt is easy to support the filaments at the terminal end of the tube on short stiff lead-in conductors through the stems, but supports for the opposite or outer ends of the filaments are not so simple. The outer ends cannot easily be braced against the grid or anode partly becaus of assembly difficulties in manufacture and partly because there are no commercial insulators available which have satisfactory high-voltage high-irequency characteristics at the operating temperatures.

One of the more common outer-end supports comprises a heavy rod anchored firmly in the stem or terminal portion of thetube and extended coaxially of the tube, each filament wire being attached to the periphery of a transverse metal disc which is centered on the outer end of the support rod. In attempts to prevent bowing and buckling due to expansion and contraction of the filamerits, the inclusion of springs at the outer ends of the cathode filaments has been tried, but degassing and exhausting temperatures usually take the temper out of the springs. Furthermore, sticking between parts that are intended to slide cause, rather than prevent, bowing.

One of the objects of our invention, accordingly, is to provide improved cathode assemblies for electron discharge devices.

Another object is to provide a filamentary cathode for power tubes which maybe closely held in position and which will not bow or buckle.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a view partly in longitudinal section of our cathode assembly;

Fig. 2 is a bottom plan view of the outer or depending end of the assembly shown in Fig. l; and

Fig. 3 is a plan view of a spider member used in the assembly.

The cathode illustrated by way of example comprises a plurality of hairpin filaments l, the

ill

legs of the filaments being symmetrically spaced about the centerline of the cathode structure. One leg ofeach filament I is solidly attached at its base end to a rod '2 which is welded or brazed to the peripheral portion of a'metal plate 3. The base end of the filament l and one end of the rod 2 are securely held together by means -of a sleeve 4 of molybdenum or other suitable metal which is wrapped about and welded thereto. The other leg of the filament issimilarly attached to a'second metal plate 5. This method or attachment insures satisfactory conduction and a strong end connection for the filaments I. The rim of the plate 3 is serrated to accommodate, without touching, the filaments legs secured to the plate '1 and 8, respectively.

A center support rod 9 is coaxial with the oathode structure and is loosely mounted at its base end through a support plate 10 which is mounted With insulating grommets on terminal p ns of the tube. A spring H encircles the base end of the center rod 9 and exerts continuous pressure urging awayfrom and in a" direction normal to the plate ID. This pressure is transmitted by the rod 9 to a metallic plate 12 which is received on a reduced portion of the outer end l3 of the 'rod for the purpose or keeping the cathode filaments under tension and in their proper alignment.

Loosely fitted upon the outer end 13 of the center rod 9 and overlyin plate I? is a spider shaped member l4, and spaced adjacent thereto isl'a' thin annular, light-weight heat shield E5. The spider l4 comprises a center disc portion having a plurality of uniformly spaced arms It extending radially from the periphery thereof. The spider shaped member l5 and shield K5 are loosely secured together by the arms It, the shield functioning also to prevent the arms from unfolding under the intense heat of the filament. The width of the arms I5 is slightly less than the length of the hairpin bight and the space between the arms l6 at the periphery of plate i2 is determined by the desired spacing between the filaments I.

In assembling, after the center rod 9 has been mounted in place, the metallic plate I2 is placed onto the outer end 13 of the rod. The spider M with its arm l6 bent substantially as indicated in broken lines at l8, Fig. 1, is then placed on the outer end l3 of the rod 9 in overlapping relation to plate l2. The filaments l are then hooked over the arm l6 and secured to the rods 2. After the filaments are all in place, the heat shield I5 is placed upon the arms l6 and the ends of the arms bent about the inner edge of the shield so as to grip and hold the shield in spaced relation to the ends of the filaments, the heat shield at the same time operating to retain the arms in their folded relation.

While the shield I5 is shown in the present embodiment, it may, of course, be omitted in which case the second fold of the arms l6 will be omitted. Furthermore, in some tube structures the support rod 9 may be omitted, the plate l2 being secured at its center to the spider H, such as by spot welding or other suitable means, the legs of the spider being free to pivot relative with respect to the plate l2 in response to unequal lengths or expansion and contraction of filaments l. l

The connection between the filaments and the arms I 6 permits the filament bight to pivot freely therein so that any unequal expansion or contraction of the several filaments is compensated by a bending or knee action movement of the bent portions l'l. This bending of the arm away from or toward the heat shield is in alignment lengthwise of the filament thereby greatly minimizing an tendency of the filament to bow or buckle. While action of the spring H on the center rod accommodates for large changes in the length of the cathode filaments, as when the temperature of the filaments is increased from room to operating temperature, the anchor connection of each bight and the flexibility of each arm together with the loose fit of plate l2 accommodate inequalities in filament expansion and contraction.

The cathode of our invention obviated the complications and expense of welding at the outer ends of the filaments, has no sticking metal-t0- metal sliding contacts, and will hold the filaments accurately in place without bowing or buckling.

Elimination of springs and many of the metal and insulating parts heretofore thought necessary not only simplifies the structure but simplifies degassing and exhaust.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention.

What is claimed is:

1. A cathode assembly comprising a cylindrical assembly of parallel filaments, a support rod 00.- axial with said assembly, a member having a plurality of radically extended arms positioned on the outer end of said rod, means cooperating with said arms to uniformly space' aid filaments radially from the end of said rod, a shield mounted on folded end portions of said arms holding said shield in spaced relation to the ends of said filaments.

2. A cathode assembly according to claim 1 wherein said filaments are of the hairpin type and said arms are threaded between the legs of the hairpin filaments, said arms being bent about the bight portions of the filaments and extended therefrom to support said shield.

3. A cathode assembly according to claim 2 wherein said shield is annular in shape and the ends of said arms are disposed in overlapping relation with respect to the inner edge of said shield.

4. A cathode structure comprising a spider shaped member having circumferentially spaced arms, a plurality of hairpin shaped filaments, an annularly shaped heat shield, the bights of said hairpin filaments being at least partially encircled by the arms of said spider shaped member, and the arms of said spider shaped member being provided with a reverse bend in overlapping relation with the inner edges of said heat shield.

5. A cathode structure comprising a stem, a plurality of lead-in conductors sealed in said stem, a pair of plates disposed transversely of said conductors and electrically connected to different ones thereof, a rod extending centrally through said plates, a spring urging said rod in a direction axially thereof, a plate disposed on said rod near the outer end thereof, a spider shaped member also disposed on the outer end of said rod, said member having symmetrically spaced arms, a plurality of hairpin filamentary cathodes, the bight of each cathode being partially encircled by an aim of said spider shaped member, a heat shield, and at least certain of said arms being provided with a reverse bend engaging and supporting said shield.

6. A cathode assembly comprising a plurality of circularly disposed filaments 0f the hairpin type, a member having a plurality of radially disposed arms, means including a fold in said arms to at least partially encircle the bights of said hairpin filaments to uniformly space said filaments at the outer ends thereof, an annular member, and the ends of said arms being folded in a reverse relation at least partially about said annular member, whereby the arms are retained against unfolding from the bights of said filements.

LYLE A. BACKER. WILLIAM H. HAPPE, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED $TATES PATENTS Number Name Date 2,419,124 Dailey Apr. 15, 1947 2,441,349 Eitel et a]. May 11, 1948 

